It is known for light to be produced by light emitting diodes (LEDs) or similar devices. LEDs naturally produce light of a specific color. It has been proposed to combine a blue LED with a phosphor that down-converts some of the blue light to longer wavelengths, but that is inefficient and produces heat, and the light produced is not considered sufficiently white light for all purposes.
It has therefore been proposed to use multiple LEDs of different colors, with or without phosphor down-conversion. In order to produce white light, it is then necessary both to balance the intensities of the different colored LEDs, and to homogenize the light from the different colored LEDs, to whatever standard of uniformity and whiteness is required for a particular application.
In the above-mentioned co-pending U.S. patent application Ser. No. 13/821,823 there is taught a novel optic named the “shell integrator” that can homogenize an array of light sources without substantially increasing the étendue of the output beam from that of the original array.
The optical architecture taught in this co-pending patent application does improve the homogeneity of the light with regard to color and luminance. However, when a shell integrator is used in a tunable light engine, it would be desirable to determine the degree of uniformity of output of the light engine and its spectral characteristics so that adjustments can be made to achieve the desired output. It would also be desirable to be able to detect when one or more of the light-source components have either failed or have changed characteristics. Finally, it would desirable that the above enhancements to the light engine be enabled through the addition of an optical feature that can be easily incorporated into a shell mixer optic, or other primary optical elements used in conjunction with an array of light sources. Ideally this feature should have minimal negative effect on the efficiency, color mixing and luminance of the light engine. Finally, this “feedback” feature should be able to interface and work well with light sensors.